1. Field of the Invention
The present invention relates in general to a rotary transformer circuit for a video cassette recorder, and more particularly to a single channel rotary transformer circuit for switching a plurality of magnetic heads. The magnetic heads travel over tracks of a magnetic tape in order to record signals on the magnetic tape, to play back signals recorded on the magnetic tape, and to transmit recording/playback signals to/from the magnetic heads through a single channel.
2. Description of the Prior Art
Generally, a rotary transformer circuit is used in a recording/playback system such as a video cassette recorder (referred to hereinafter as VCR), a camcorder, a digital audio tape recorder and etc. to transmit signals read from a plurality of magnetic heads to a plurality of head amplifiers. Such a conventional rotary transformer circuit comprises a plurality of rotary transformers, each of which has a rotor and a stator. The rotor and stator have a free space in the order of several tens of .mu.m therebetween, in which are formed channel grooves corresponding to the number of channels and a short ring groove into which a short ring is mounted to reduce an inter-channel signal interference.
In a playback mode, the rotor rotates to transfer a signal read from a corresponding one of the magnetic heads to the stator, which then transmits the signal from the rotor to a playback pre-amplifier through a coil. In a recording mode, a signal from a recording amplifier is transferred from the stator to the rotor.
Referring to FIG. 1, there is shown a schematic block diagram of a conventional multi-channel rotary transformer circuit for a VCR. As shown in this drawing, the conventional multi-channel rotary transformer circuit comprises a head section 10, a rotary transformer section 20, a head amplification section 30, a channel switching section 40 and a microcomputer 50.
The head section 10 includes a plurality of magnetic heads a-d for recording signals on a magnetic tape (not shown) and playing back signals recorded on the magnetic tape.
The rotary transformer section 20 is adapted to transfer output signals from the head section 10 to the head amplification section 30. Also, the rotary transformer section 20 transfers output signals from the head amplification section 30 to the head section 10. To this end, the rotary transformer section 20 includes a plurality of rotary transformers 21-24 of channels of the number equal to that of the magnetic heads a-d in the head section 10. Each of the rotary transformers 21-24 connects a corresponding one of the magnetic heads a-d in the head section 10 to a corresponding one of a plurality of recording/playback amplifier circuits 31-34 in the head amplification section 30. Each of the records/playback amplifier circuits 31-34 includes an amplifier.
Each of the recording/playback amplifiers 31-34 in the head amplification section 30 amplifies an output signal from the corresponding one of the rotary transformers 21-24 in the rotary transformer section 20 by a predetermined level and outputs the amplified signal to the channel switching section 40. Each of the recording/playback amplifier circuits 31-34 also transfers an output signal from the channel switching section 40 to the corresponding one of the rotary transformers 21-24 in the rotary transformer section 20.
The microcomputer 50 is adapted to generate a switching pulse signal in response to a drum pulse signal which is generated by a servo circuit (not shown) whenever a drum rotates once. The microcomputer 50 outputs the generated switching pulse signal to the channel switching section 40.
The channel switching section 40 is switched in response to the switching pulse signal from the microcomputer 50 to transfer a selected one of the output signals from the head amplification section 30 to a video/audio processing circuit (not shown). Also, the channel switching section 40 is switched in response to the switching pulse signal from the microcomputer 50 to transfer an output signal from the video/audio processing circuit to the head amplification section 30. To this end, the channel switching section 40 includes switches 41 and 42.
The operation of the conventional multi-channel rotary transformer circuit for the VCR with the above-mentioned construction will hereinafter be described with reference to FIGS. 2A to 2H which are waveform diagrams of the output signals from the components in FIG. 1.
First, in the playback mode, the magnetic heads a-d in the head section 10 travel on tracks of the magnetic tape to read sequentially the signals recorded on the magnetic tape. Then, the magnetic heads a-d output the read signals to the rotary transformers 21-24 in the rotary transformer section 20, respectively. The rotary transformers 21-24 transfer the output signals from the magnetic heads a-d to the recording/playback amplifier circuits 31-34 in the head amplification section 30, respectively. Each of the recording/playback amplifier circuits 31-34 amplifies the output signal from the corresponding one of the rotary transformers 21-24 in the rotary transformer section 20 by the predetermined level and outputs the amplified signal to the channel switching section 40.
The switching pulse signal as shown in FIG. 2A is applied from the microcomputer 50 to the channel switching section 40. When the switching pulse signal from the microcomputer 50 is low in logic, movable terminals of the switches 41 and 42 in the channel switching section 40 are connected to one of the terminals thereof as shown by solid lines in FIG. 1. As a result, the output signals from the magnetic heads a and c are selected as shown in FIGS. 2B and 2C and combined as shown in FIG. 2D. The combined signal as shown in FIG. 2D is then transferred to an input/output terminal by the switches 41 and 42. On the contrary, in the case where the switching pulse signal from the microcomputer 50 is high in logic, the movable terminals of the switches 41 and 42 are connected to the other terminals thereof as shown by dotted lines in FIG. 1. As a result, the output signals from the magnetic heads b and d are selected as shown in FIGS. 2E and 2F and combined as shown in FIG. 2G. The combined signal as shown in FIG. 2G is then transferred to the input/output terminal by the switches 41 and 42.
In result, a radio frequency (referred to hereinafter as RF) signal as shown in FIG. 2H is transferred to the video/audio processing circuit (not shown) through the input/output terminal in response to the switching pulse signal as shown in FIG. 2A.
On the other hand, in the recording mode, a recording signal as shown in FIG. 2H is applied from the video/audio processing circuit (not shown) to the channel switching section 40 through the input/output terminal. At this time, the switches 41 and 42 in the channel switching section 40 are switched in a similar manner to the playback mode in response to the switching pulse signal from the microcomputer 50. As a result, the signals as shown in FIGS. 2B, 2C, 2E and 2F are transferred from the switches 41 and 42 to the recording/playback amplifiers 31-34 in the head amplification section 30, respectively. Then, the signals as shown in FIGS. 2B, 2C, 2E and 2F are amplified by the recording/playback amplifier circuits 31-34 in the head amplification section 30 and transferred through the rotary transformers 21-24 in the rotary transformer section 20 to the magnetic heads a-d in the head section 10, respectively. In result, travelling on the tracks of the magnetic tape, the magnetic heads a-d record sequentially the transferred signals on the magnetic tape.
However, in the above-mentioned conventional multi-channel rotary transformer circuit for a VCR, a signal-to-noise (S/N) ratio is degraded due to an inter-channel signal interference resulting from an increase in the number of channels because each magnetic head corresponds to one channel. Also, a short ring must be designed to shield the inter-channel signal interference. Further, the number of the head amplifiers being used is the same as that of the magnetic heads, resulting in a complexity in the manufacturing process and an increase in the manufacturing cost.